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/ N. V. Erkaev [et al.] // Geophys. Res. Lett. - 2012. - Vol. 39. - Ст. L01103, DOI 10.1029/2011GL050209. - Cited References: 16. - This work was done while NVE was on a research visit to the Space Science Center of UNH. This work is supported by RFBR grant N 09-05-91000-ANF_a, and also by the Austrian "Fonds zur Forderung der wissenschaftlichen Forschung" under Project I 193-N16 and the "Verwaltungsstelle fur Auslandsbeziehungen" of the Austrian Academy of Sciences. Work by CJF was supported by NASA grants NNX10AQ29G and NNX08AD11G. . - ISSN 0094-8276РУБ Geosciences, Multidisciplinary

Аннотация: In previous work we used a semi-analytical treatment to describe accelerated magnetosheath flows caused by the draping of interplanetary magnetic field (IMF) lines around the magnetosphere. Here, we use the same approach, i.e., modeling the magnetic field lines as elastic strings, to examine how the magnetic tension force, one of the two agents responsible for producing these flows, varies along field lines away from the equatorial plane. The bend in the field line caused by the draping mechanism propagates as two oppositely-directed waves to higher latitudes. For a due northward IMF - the case we consider here - these propagate symmetrically north/south of the equatorial plane. As a result, a two-peaked latitude velocity profile develops as we go further downtail and the velocity peaks migrate along the magnetic field line to higher latitudes. We examine this velocity-profile for two Alfven Mach numbers (M-A = 8 and 3), representative of conditions in the solar wind at 1 AU ("normal" solar wind and solar transients). Qualitatively, the picture is the same but quantitatively there are important differences: (i) the flows reach higher values for the lower M-A (maximum V/V-SW = 1.6) than for the higher M-A (V/V-SW = 1.3); (ii) asymptotic values are reached farther downstream of the dawn-dusk terminator for the lower M-A (similar to-50 R-E vs -15 R-E); (iii) For the lower M-A the highest speeds are reached away from the equatorial plane. We predict two channels of fast magnetosheath flow next to the magnetopause at off-equatorial latitudes that exceed the solar wind speed. Citation: Erkaev, N. V., C. J. Farrugia, A. V. Mezentsev, R. B. Torbert, and H. K. Biernat (2012), Accelerated magnetosheath flows caused by IMF draping: Dependence on latitude, Geophys. Res. Lett., 39, L01103, doi:10.1029/2011GL050209.

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Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Farrugia, C.J.; Mezentsev, A.V.; Torbert, R.B.; Biernat, H.K.

[Text] / B.Harris [et al.] // Ann. Geophys. - 2013. - Vol. 31, Is. 10. - P1779-1789, DOI 10.5194/angeo-31-1779-2013. - Cited References: 26. - Work at UNH is supported by NASA Grants NNX10AQ29G and NNX13AP39G. N. V. Erkaev is supported by grant No. 12-05-00152-a from the Russian Foundation of Basic Research. . - ISSN 0992-7689РУБ Astronomy & Astrophysics + Geosciences, Multidisciplinary + Meteorology & Atmospheric Sciences

Аннотация: Acceleration of magnetosheath plasma resulting from the draping of the interplanetary magnetic field (IMF) around the magnetosphere can give rise to flow speeds that exceed that of the solar wind (V-SW) by up to similar to 60%. Three case event studies out of 34 identified events are described. We then present a statistical study of draping-related accelerations in the magnetosheath. Further, we compare the results with the recent theory of Erkaev et al. (2011, 2012). We present a methodology to help distinguish draping-related accelerations from those caused by magnetic reconnection. To rule out magnetopause reconnection at low latitudes, we focus mainly on the positive B-z phase during the passage of interplanetary coronal mass ejections (ICMEs), as tabulated in Richardson and Cane (2010) for 1997-2009, and adding other events from 2010. To avoid effects of high-latitude reconnection poleward of the cusp, we also consider spacecraft observations made at low magnetic latitudes. We study the effect of upstream Alfven Mach number (M-A) and magnetic local time (MLT) on the speed ratio V/V-SW. The comparison with theory is good. Namely, (i) flow speed ratios above unity occur behind the dawn-dusk terminator, (ii) those below unity occur on the dayside magnetosheath, and (iii) there is a good general agreement in the dependence of the V ratio on M-A.


Доп.точки доступа:
Harris, B.; Farrugia, C.J.; Erkaev, N.V.; Еркаев, Николай Васильевич; Torbert, R.B.; NASA [NNX10AQ29G, NNX13AP39G]; Russian Foundation of Basic Research [12-05-00152-a]

[Text] / N. V. Erkaev, C. J. Farrugia, H. K. Biernat // Planet Space Sci. - 2003. - Vol. 51, Is. 12. - P745-755, DOI 10.1016/S0032-0633(03)00111-9. - Cited References: 36 . - ISSN 0032-0633РУБ Astronomy & Astrophysics

Аннотация: The magnetized solar wind carries a large amount of energy but only a small fraction of it enters the magnetosphere and powers its dynamics. Numerous observations show that the interplanetary magnetic field (IMF) is a key parameter regulating the solar wind-magnetosphere interaction. The main factor determining the amount of energy extracted from the solar wind flow by the magnetosphere is the plasma flow structure in the region adjacent to the sunward side of the magnetopause. While compared to the energy of the solar wind flow the IMF magnetic energy is relatively weak, it is considerably enhanced in a thin layer next to the dayside magnetopause variously called the plasma depletion layer or magnetic barrier. Important features of this barrier/layer are (i) a pile-up of the magnetic field with (ii) a concurrent decrease of density, (iii) enhancement of proton temperature anisotropy, (iv) asymmetry of plasma flow caused by magnetic field tension. and (v) characteristic wave emissions (ion cyclotron waves). Importantly, the magnetic barrier can be considered as an energy source for magnetic reconnection. While the steady-state magnetic barrier has been extensively examined, non-steady processes therein have only been addressed by a few authors. We discuss here two non-steady aspects related to variations of the magnetic barrier caused by (i) a north-to-south rotation of the IMF, and (ii) by pulses of magnetic field reconnection at the magnetopause. When the IMF rotates smoothly from north-to-south, a transition layer is shown to appear in the magnetosheath which evolves into a thin layer bounded by sharp gradients in the magnetic field and plasma quantities. For a given reconnection rate and calculated parameters of the magnetic barrier, we estimate the duration and length scale of a reconnection pulse as a function of the solar wind parameters. Considering a sudden decrease of the magnetic field near the magnetopause caused by the reconnection pulse, we study the relaxation process of the magnetic barrier. We find that the relaxation time is longer than the duration of the reconnection pulse for large Alfved-Mach numbers. (C) 2003 Elsevier Ltd. All rights reserved.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Farrugia, C.J.; Biernat, H.K.

[Text] / H. K. Biernat [et al.] // Nonlinear Process Geophys. - 2000. - Vol. 7: 24th General Assembly of the European-Geophysical-Society (APR 19-23, 1999, THE HAGUE, NETHERLANDS), Is. 03.04.2013. - P201-209. - Cited References: 34 . - ISSN 1023-5809РУБ Geochemistry & Geophysics + Meteorology & Atmospheric Sciences

Аннотация: The study of the interaction of the solar wind with magnetized and unmagnetized planets forms a central topic of space research. Focussing on planetary magnetosheaths, we review some major developments in this field. Magnetosheath structures depend crucially on the orientation of the interplanetary magnetic field, the solar wind Alfven Mach number, the shape of the obstacle (axisymmetric/non-axisymmetric, etc.), the boundary conditions at the magnetopause (low/high magnetic shear), and the degree of thermal anisotropy of the plasma. We illustrate the cases of Earth, Jupiter and Venus. The terrestrial magnetosphere is axisymmetric and has been probed in situ by many spacecraft. Jupiter's magnetosphere is highly non-axisymmetric. Furthermore, we study magnetohydrodynamic effects in the Venus magnetosheath.


Доп.точки доступа:
Biernat, H.K.; Erkaev, N.V.; Еркаев, Николай Васильевич; Farrugia, C.J.; Vogl, D.F.; Schaffenberger, W.

[Text] / C. J. Farrugia, N. V. Erkaev, H. K. Biernat // J. Geophys. Res-Space Phys. - 2000. - Vol. 105, Is. A1. - P115-127, DOI 10.1029/1999JA900350. - Cited References: 26 . - ISSN 0148-0227РУБ Astronomy & Astrophysics

Аннотация: We apply our recent three-dimensional anisotropic MHD model of magnetosheath flow [Erkaev et al., 1999] to study quantitatively effects of solar wind dynamic pressure (P-d infinity) and Alfven Mach number (M-a infinity) on the anisotropic magnetosheath and the plasma depletion layer (PDL) in the subsolar region. Given the wide range over which these two parameters vary, their influence on the magnetosheath structure may be significant. Our analysis is applicable to quasisteady changes in the interplanetary medium. Following our earlier work; and in general agreement with the data, we define the sunward edge of the PDL by beta(parallel to) = 1, where pll is the proton beta parallel to the magnetic field. We first discuss changes in P-d infinity occurring under constant M-a infinity. In this case, a rescaling of the parameters yields the effects on the magnetosheath. We then study quantitatively a changing dynamic pressure through a varying Alfven Mach number. We obtain profiles of key magnetosheath parameters and the width of the PDL for Alfven Mach numbers representative of the solar wind at Earth orbit. Gradients in parameter profiles become steeper and shift toward the magnetopause as M-a infinity increases. We find that PDL width varies as 1/M-a infinity(2) even in the anisotropic magnetosheath. Using our model to study the magnetosheath location where the electromagnetic ion cyclotron wave (EICW) instability dominates over the mirror instability, we find that this location occurs well inside the PDL. In addition, we estimated the fraction of the PDL width occupied by the EICWs as a function of solar wind Alfven Mach number. We conclude that the EICW regime is contained in, but is not co-extensive with, the PDL. Examining critically this issue by changing the PDL identification criterion to others based on a density decrease relative to the bow shock value and a systematic drop toward the magnetopause, we find that this result still holds, but the region where EICWs are destabilized occupies a different fraction of the PDL thus defined. Some model results are compared with documented data from an inbound crossing of the magnetosheath made on December 24, 1994. Good agreement with model predictions are obtained.


Доп.точки доступа:
Farrugia, C.J.; Erkaev, N.V.; Еркаев, Николай Васильевич; Biernat, H.K.

[Text] / H. K. Biernat, N. V. Erkaev, C. J. Farrugia // J. Geophys. Res-Space Phys. - 1999. - Vol. 104, Is. A6. - P12617-12626, DOI 10.1029/1999JA900032. - Cited References: 37 . - ISSN 0148-0227РУБ Astronomy & Astrophysics

Аннотация: We describe the "magnetic string" approach to integrating the dissipationless magnetohydrodynamic (MHD) equations for flow around planetary obstacles and apply it to some aspects of the flow in the magnetosheath of Venus. Our method has both analytical and numerical components and is particularly suited to study the structure of the magnetic barrier (depletion layer). We do not include ion pickup processes and thus discuss only the contribution to the structure of the Venus magnetosheath made by the flow of the shocked solar wind. We work with an interplanetary magnetic field which is directed orthogonal to the solar wind bulk velocity. Magnetic forces on the flow are strongly dependent on the Alfven Mach number upstream of the bow shock, and one aim of this work is to study the dependence of field and flow quantities in the Venus magnetosheath on this parameter, thus allowing further future comparisons with data under a variety of interplanetary conditions. A second aim is to compare our MHD model results to a? synopsis of observations made by the Pioneer Venus Orbiter. As one main conclusion, we show that this method leads, in principle, to a standoff bow shock position in good agreement with observations. We find, namely, that for a low but reasonable Alfven Mach number, our MHD-modeled magnetosheath is only similar to 3.6% thinner in the Sun-Venus direction than that given by observations. Our method is complementary to three-dimensional, global MHD simulations of the solar wind-Venus interaction and offers versatility to modeling other aspects of the complicated interaction of the solar wind with Venus.


Доп.точки доступа:
Biernat, H.K.; Erkaev, N.V.; Еркаев, Николай Васильевич; Farrugia, C.J.

[Text] / N. V. Erkaev, C. J. Farrugia, H. K. Biernat // J. Geophys. Res-Space Phys. - 1999. - Vol. 104, Is. A4. - P6877-6887, DOI 10.1029/1998JA900134. - Cited References: 29 . - ISSN 0148-0227РУБ Astronomy & Astrophysics

Аннотация: We present a three-dimensional, one-fluid, steady state magnetohydrodynamic (MHD) model of magnetosheath flow near the subsolar line with unequal plasma pressures perpendicular (P-perpendicular to) and parallel (P-parallel to) to the magnetic field (P-perpendicular to P-parallel to) Aside from an assumption on the total pressure normal to the magnetopause, our analytical-numerical method is completely general and is an extension of our isotropic, "magnetic string" MHD model, which we describe in detail here. The MHD equations are closed by a relation between P-perpendicular to and P-parallel to as in the Bounded Anisotropy Model [Denton et al., 1994] corresponding to the threshold of the electromagnetic proton cyclotron wave instability. We take an IMF oriented perpendicular to the solar wind velocity. As boundary conditions, we have Rankine-Hugoniot relations at the bow shock and a no-flow condition at the magnetopause. We obtain steady state profiles of the magnetic field and plasma parameters for upstream sonic and Alfven Mach numbers equal to 10, and compare them with the isotropic case (P-parallel to = P-perpendicular to). Anisotropy slightly thickens the magnetosheath. In the anisotropic model, the density, the parallel and perpendicular temperatures, plasma pressures, and betas all decrease toward the magnetopause. Isotropic profiles lie between those of quantities perpendicular and parallel to the field. Anisotropy has considerable effect on the density profile, which lies below that in the isotropic limit throughout the magnetosheath. Density depletion results from stretching of magnetic field lines, which is caused by field-aligned plasma flow. Approaching the magnetopause, the tangential component of velocity parallel to the magnetic field decreases, while the tangential component perpendicular to the magnetic field increases. These are features characterizing a stagnation line flow at the magnetopause. The acceleration along the magnetic field is produced by the gradient of P-parallel to and the mirror force, which depends on anisotropy. They both make substantial contributions and are responsible for the changes we see;from isotropy. The acceleration perpendicular to magnetic field is also larger than in the case of isotropy and is caused by the gradient of total pressure, the magnetic strength, and the mirror force. In addition, acceleration in both directions is affected by the decreasing density.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Farrugia, C.J.; Biernat, H.K.

[Text] / C. J. Farrugia [et al.] // J. Geophys. Res-Space Phys. - 1997. - Vol. 102, Is. A6. - P11315-11324DOI 10.1029/97JA00410. - Cited References: 29 . - РУБ Astronomy & Astrophysics

Аннотация: Together with the magnetic shear across the magnetopause, the solar wind Alfven Mach number, M-A infinity plays a central role in determining the structure of the magnetosheath. Recent theoretical modeling has shown, in particular, that as M-A infinity decreases, the region adjacent to the sunward side of the magnetopause where the interplanetary magnetic field (IMF) exerts a strong influence on the flow (i.e., the so-called ''plasma depletion layer''), is no longer confined to a thin layer similar to 0.3 Earth radii (R-E) thick but occupies an increasingly larger fraction of the magnetosheath. Furthermore, the model predicts the possibility of a plasma depletion layer for low M-A infinity, irrespective of the size of the magnetic shear at the magnetopause, In this paper we study three examples of low latitude ISEE 2 passes through the dayside magnetosheath near noon: December 3, 1979; October 5, 1979; and November 11, 1979, In all three examples, MA, was lower than normal. During the December 3 pass (which we treat qualitatively), we find evidence of a plasma depletion layer when the IMF was pointing south, On the other two passes (which we study quantitatively), the interplanetary magnetic field was strongly northward pointing, leading to low magnetic shear at the respective magnetopause crossings, The October 5 pass was under steady interplanetary conditions and we find good agreement between theory and data, Temporal variations of the interplanetary medium during the November 11 pass necessitated an extension of the steady state theory to encompass piecewise steady (on average) interplanetary conditions, Better agreement with the data results when the theory is extended further to correct the total pressure at the sunward side of the magnetopause by integrating the magnetic tension term across the layer. For wide plasma depletion layers, this correction can be substantial.


Доп.точки доступа:
Farrugia, C.J.; Erkaev, N.V.; Еркаев, Николай Васильевич; Biernat, H.K.; Lawrence, G.R.; Elphic, R.C.

[Text] / N. V. Erkaev [et al.] // Geophys. Res. Lett. - 2011. - Vol. 38. - Ст. L01104, DOI 10.1029/2010GL045998. - Cited References: 20. - This work was done while N.V.E. was on a research visit to the Space Science Center of UNH. This work is supported by RFBR grant N 09-05-91000-ANF_a and also by the Austrian "Fonds zur Forderung der wissenschaftlichen Forschung" under project I 193-N16 and the "Verwaltungsstelle fur Auslandsbeziehungen" of the Austrian Academy of Sciences. Work by C.J.F. was supported by NASA grants NNX10AQ29G and NNX08AD11G. . - ISSN 0094-8276РУБ Geosciences, Multidisciplinary

Аннотация: We study the acceleration of magnetosheath plasma using a semi-analytical magnetic string approach for a range of solar wind Alfven Mach numbers, M-A, between 2 and 20. We work with an IMF vector perpendicular to the solar wind velocity, V-sw, and pointing north. We do not invoke magnetic reconnection. Our results indicate that magnetosheath speeds can exceed the solar wind speed, and the ratio V/V-sw increases with decreasing M-A. Analyzing the dependence of this ratio on M-A, we find that for M-A = 2, maximum V/V-sw approximate to 1.6, and for M-A = 10-20, maximum V/V-sw varies from 1.21 to 1.13. Maximum speeds occur a few Earth radii (R-E) tailward of the dawn-dusk terminator. The thickness of the accelerated flow layer varies as M-A(-2). Taking the magnetopause subsolar distance as 10 R-E, we find typical values for the thickness of similar to 4 R-E for M-A = 3 and 0.35 R-E for M-A = 10. The physical mechanism is that of draping of the magnetic field lines around the magnetosphere, and the associated magnetic tension and total pressure gradient forces acting on the flow. For lower M-A the plasma depletion is stronger, and thus the acceleration produced by the pressure gradient is larger. An additional acceleration is produced by the magnetic tension, which is stronger for smaller M-A. At the dayside the pressure gradient and magnetic tension forces both act in the same direction. But tailward of the terminator the magnetic tension starts to act in the opposite direction to the pressure gradient. When the resulting force vanishes, the highest speed is attained. Citation: Erkaev, N. V., C. J. Farrugia, B. Harris, and H. K. Biernat (2011), On accelerated magnetosheath flows under northward IMF, Geophys. Res. Lett., 38, L01104, doi: 10.1029/2010GL045998.


Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Farrugia, C.J.; Harris, B.; Biernat, H.K.